In 1979, I made a program called VisiBase in this BASIC.
It's a visual database modeled after VisiCalc.
That won me a joystick in at a competition by the local computer store. :-)
Still have the source, that works in an Apple 2 emulator. It's 13 K in ASCII (untokenized).
From the video [1] that links to Ben Eater's fork with extensions and configuration specific to his 6502 breadboard computer [2]. That in turn is forked from `mist64/msbasic` which refers to a blog post [3] which states:
> This episode of “Computer Archeology” is about reverse engineering eight different versions of Microsoft BASIC 6502 (Commodore, AppleSoft etc.), ...
> This article also presents a set of assembly source files that can be made to compile into a byte exact copy of seven different versions of Microsoft BASIC, and lets you even create your own version.
So Ben Eater's version is based on a reverse engineered version of the same program. You should be able to adapt the code released here to run on Ben Eater's 6502 with a bit of work.
Sadly nothing in Scott's blog post about how they obtained the source. Was it still in Microsoft's archives? Did they happen upon some tractor-feed print-outs they had to type in by hand?
It would also be interesting why it was open-sourced now. I assume if they had done the same last year, the resulting loss of revenue would not have destroyed the plucky little $3T upstart.
No, there was a big post somewhere on the previous release two weeks ago of the DOS source showing just how incredibly hard of a challenge it was to properly input/OCR all the reams of source was.
This source is a lot smaller, but still annoying if they had to type it all in or OCR it.
The Apple ][ basic interpreter placed its "get next token" routine down in the first 255 bytes of the computer's memory. Being there allowed for the machine instructions to be fetched twice as fast as "high memory". And "get next token" is definitely a good guess for hotpath.
I have a copy of "Tiny" Pascal by Supersoft from 1979 on a cassette tape which was licensed to Tandy Corp and which would load onto a 16KB TRS-80 Model III and allow a bit of room for programming.
One of the great regrets of my life is that when I was doing so and when it would have mattered, I was unaware of the patch for this which would have allowed it to be saved as an executable to a TRS-DOS disk....
Microsoft itself popularized BASIC on microcomputers with its 8080 BASIC, starting on the Altair and ported to everything with A, B, C, D, E, H, and L registers since.
Before then, however, BASIC was already popular on minicomputers as both an introductory language for beginners and a business language; the various "Business BASIC" dialects providing a small-business alternative to COBOL on mainframes with their features for decimal math and ISAM database access.
Except that wasn't possible. Languages like BASIC and Forth exist because they were the only kind of language implementable in 4K with no disk. Pascal in its smallest form (UCSD p-system) still needed disk overlays. The smallest C compilers were poly phase, needing storage for intermediate state.
I am really torn about this. Sure Microsoft is doing a lot of open source today (.NET core, VS Code and a bit of historic curiosities such as this one) but the "open letter to the hobbyists" still stands :) Release the Windows source code then we are talking.
In 1979, I made a program called VisiBase in this BASIC. It's a visual database modeled after VisiCalc. That won me a joystick in at a competition by the local computer store. :-) Still have the source, that works in an Apple 2 emulator. It's 13 K in ASCII (untokenized).
Please, put it in a public git somewhere!
Ben Eater's 6502 series [1] uses MSBASIC for programming along with WozMon as the terminal interface.
[1] https://www.youtube.com/playlist?list=PLowKtXNTBypFbtuVMUVXN...
Is that the same BASIC as this?
From the video [1] that links to Ben Eater's fork with extensions and configuration specific to his 6502 breadboard computer [2]. That in turn is forked from `mist64/msbasic` which refers to a blog post [3] which states:
> This episode of “Computer Archeology” is about reverse engineering eight different versions of Microsoft BASIC 6502 (Commodore, AppleSoft etc.), ...
> This article also presents a set of assembly source files that can be made to compile into a byte exact copy of seven different versions of Microsoft BASIC, and lets you even create your own version.
So Ben Eater's version is based on a reverse engineered version of the same program. You should be able to adapt the code released here to run on Ben Eater's 6502 with a bit of work.
[1] https://www.youtube.com/watch?v=XlbPnihCM0E&list=PLowKtXNTBy...
[2] https://github.com/beneater/msbasic
[3] https://www.pagetable.com/?p=46
Previous discussion:
Microsoft BASIC for 6502 Microprocessor – Version 1.1 - https://news.ycombinator.com/item?id=45118392 - Sept 2025 (198 comments)
Related ongoing thread:
Microsoft open-sources "the earliest DOS source code discovered to date" - https://news.ycombinator.com/item?id=48253386 - May 2026 (110 comments)
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Sadly nothing in Scott's blog post about how they obtained the source. Was it still in Microsoft's archives? Did they happen upon some tractor-feed print-outs they had to type in by hand?
It would also be interesting why it was open-sourced now. I assume if they had done the same last year, the resulting loss of revenue would not have destroyed the plucky little $3T upstart.
I assume today typing in by hand is no longer needed, with text parsing from images being table stakes for LLMs.
No, there was a big post somewhere on the previous release two weeks ago of the DOS source showing just how incredibly hard of a challenge it was to properly input/OCR all the reams of source was.
This source is a lot smaller, but still annoying if they had to type it all in or OCR it.
You don’t need an llm to do this.
Of course, but I do know that it wasn't that long ago that OCR still wasn't great for many documents. These days LLMs can tackle it all.
Maybe Apple can finally release MacBasic now that Microsoft can no longer stop licensing their Basic to the Apple II family.
I'll even send Bill Gates a dollar for that:
https://www.folklore.org/MacBasic.html
The Apple ][ basic interpreter placed its "get next token" routine down in the first 255 bytes of the computer's memory. Being there allowed for the machine instructions to be fetched twice as fast as "high memory". And "get next token" is definitely a good guess for hotpath.
I doubt the .gitignore, README.md, and SECURITY.md files were created 49 years ago, as the GitHub repo indicates :D
Ahead of their time ;-D
Do you think computing history would have been much different if Microsoft made a 6502 Pascal interpreter instead?
Pascal is a lot broader language and won't fit in sub 16KB of ROM (even if you exclude monitor [call-151])
A subset of it?
I have a copy of "Tiny" Pascal by Supersoft from 1979 on a cassette tape which was licensed to Tandy Corp and which would load onto a 16KB TRS-80 Model III and allow a bit of room for programming.
One of the great regrets of my life is that when I was doing so and when it would have mattered, I was unaware of the patch for this which would have allowed it to be saved as an executable to a TRS-DOS disk....
Maybe they could have implemented a useful subset of Pascal.
Atari 8-bits had a cut-down version of ALGOL called Action! which is now open source: https://forums.atariage.com/topic/217770-action-source-code/...
They didn't invent the language. BASIC was already a popular language for beginners on microcomputers at that time.
Microsoft itself popularized BASIC on microcomputers with its 8080 BASIC, starting on the Altair and ported to everything with A, B, C, D, E, H, and L registers since.
Before then, however, BASIC was already popular on minicomputers as both an introductory language for beginners and a business language; the various "Business BASIC" dialects providing a small-business alternative to COBOL on mainframes with their features for decimal math and ISAM database access.
Except that wasn't possible. Languages like BASIC and Forth exist because they were the only kind of language implementable in 4K with no disk. Pascal in its smallest form (UCSD p-system) still needed disk overlays. The smallest C compilers were poly phase, needing storage for intermediate state.
I am really torn about this. Sure Microsoft is doing a lot of open source today (.NET core, VS Code and a bit of historic curiosities such as this one) but the "open letter to the hobbyists" still stands :) Release the Windows source code then we are talking.
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